Isatin thiosemicarbazone derivatives as inhibitors against corrosion of AA6060 aluminium alloy in acidic chloride medium: substituent effects

Abstract Five isatin thiosemicarbazone derivatives bearing different substituents (R) at 5-position of the isatin moiety, ISA-R, being R = -H, -CH3, -F, -Cl and -NO2, were synthesized and fully characterized. The corrosion inhibition action of ISA-R on AA6060 aluminium alloy in acidic chloride medium was studied in relation to the substituent effects using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrochemical potentiodynamic polarization (PDP) and weight loss measurements. The results showed that the inhibition behaviors of ISA-R were strongly correlated with the substituent modifications. ISA-NO2 was found to possess the highest capability to increase the corrosion resistance of the alloy and ISA-Cl exhibited some inhibition efficacy, whereas the others have little action. ISA-H, ISA-F, ISA-Cl and ISA-NO2 acted as cathodic-type inhibitors, and ISA-CH3 as a mixed-type inhibitor primarily retarding the cathodic processes of the alloy in the corrosion solution. ISA-R can be adsorbed on the alloy surface as evidenced by the results of EDS and XPS. The π-electron density on the isatin ring of ISA-NO2 is more deficient over the other ISA-R, which facilitates the adsorption of ISA-NO2 and formation of a barrier film on the alloy surface, and accordingly enhances its anti-corrosive performance for the alloy.